Expanded porous thermoplastic polymer membranes and device for the production thereof

Abstract

Open celled membranes from thermoplastic polymers are prepared from foamed polymer melts by extrusion through a die.

What is claimed is:  
     
       1. In an apparatus for making a foamed porous membrane comprising an extruder equipped with a metering apparatus and heating elements to form a polymer melt, said extruder having a cylinder connected via a first melt pump to a die for extrusion of a membrane from said polymer melt, an injection stage before said first melt pump for charging said polymer melt with a cell former, a heat exchanger located between said first melt pump and said die to form a second mixing stage, the improvement comprising a second melt pump located upstream from said die for forcing said polymer melt through said die. 
     
     
       2. The apparatus of  claim 1  where said heat exchanger is equipped with a static mixer. 
     
     
       3. The apparatus of  claim 1  wherein said injection stage comprises metering pumps that are connected via hollow needles and plates so as to be in fluid communication with said cylinder of said extruder. 
     
     
       4. The apparatus of  claim 3  wherein said metering pumps are equipped with pump heads that are thermostatically controlled. 
     
     
       5. The apparatus of  claim 1  wherein said die is configured as a wide-slit nozzle.